When the edges of board-like, batten-like or similar workpieces of open-pore wood-based materials, for example chipboards, or other open-pore materials are to be processed, they have to be improved for many applications because the open-pore cut surfaces of the workpieces lack surface quality and strength. Accordingly, various processes have been developed for improving open-pore edges, for example of chipboards.
Thus, in one of their prospectuses, the Homag company describes a one-pass edge sealing process. This process is based on the filling of the voids present in the edges of wood-based materials, where they are particularly conspicuous in the middle layer, so that an uninterrupted, pore-free and smooth surface is formed. To this end, a thermoplastic filler (a hotmelt material) is applied in the form of a hot paste and pressed into the pores. The filler hardens in the following cold phase. The entire process takes place in a single pass, as known from standard edge banding machines. The surface thus formed is immediately smoothed and can be film-coated at a following station in the same machine. This one-pass process comprises the following steps:
1. Preliminary milling and shaping of the profiles. PA1 2. Application of the thermoplastic edge sealing compound by a roll-on process carried out at temperatures of 180 to 230.degree. C. and preferably at 190 to 220.degree. C. PA1 3. After application, the sealing compound is smoothed with heated metal shoes (temperature 160 to 180.degree. C.). PA1 4. After smoothing, the sealed edge is cooled with air-cooled metal shoes. PA1 5. Steps 2 to 4 are repeated so that a second layer is built up, giving a pore-free smooth edge surface. PA1 6. Milling of the cooled edge sealing compound and further edge processing, for example embossing with heat-sealing film, jacketing, postforming and printing. PA1 The compound should show good flow behavior at the processing temperature and should readily be able to be pressed into the pores of the chipboard by the roller. PA1 It should show good adhesion to the chipboard material and to itself (process steps 2 to 4 are repeated) so that no delamination occurs during the second application. PA1 In addition, the hardened compound should adhere well to heat sealing films, adhesives and printing inks. PA1 The compound should become strong and hard very quickly in process step 4 (cooling) because milling is carried out immediately afterwards. PA1 The hardened edge sealing compound should have high impact strength with no tendency towards embrittlement.
The one-pass process is carried out at speeds of 10 to 30 m/min. and preferably 15 to 25 m/min.
The thermoplastic edge sealing compound is expected to satisfy the following requirements:
Accordingly, the problem addressed by the invention was to provide a thermoplastic compound with which edges of porous wood-based materials could be improved in a one-pass process.
The solution to this problem as provided by the invention is defined in the claims and consists essentially in the selection of a thermoplastic compound according to softening point, open time and viscosity number.